1. Field of the Invention
The present invention relates to a demand control apparatus for reducing the total power used by a group of loads and a power distribution control system for distributing an electric power by transmitting and receiving signals between the terminal of an electric power company and the terminals of houses, factories and the like.
2. Description of the Related Art
Recently, many consumers have been widely attempting to save the energy by setting the maximum working power level or power demand value to suppress the total quantity of electric power consumed within the range defined by the set demand value.
The conventional demand control systems are known to be of such a type that a warning or control command is produced for a load or loads in which the input power exceeds the set power level or that any load having a larger working power is preferentially shut off, as described in Japanese Patent Laid-Open No. Sho 57-71233. There is also known a demand control apparatus which comprises a plurality of loads classified into on-off controllable loads and producing loads so that when the working power level consumed exceeds the set demand level, the number of producing loads are first reduced to control the working power level into a target level and the on-off controllable loads will be finally shut off, as described in Japanese Patent Laid-Open No. Sho 57-101526. Japanese Patent Laid-Open No. Sho 55-108048 further describes a demand control apparatus which can produce a failure signal when the total quantity of electric power consumed exceeds the target level even if all the loads to be controlled are controllably shut off.
However, the demand control apparatus described in Japanese Patent Laid-Open No. Sho 57-71283 requires the registration of an electric working power. Although the system can effectively suppress the working power level below the set demand level since any load having a larger working power is preferentially shut off, the sequence of preference cannot be changed depending on the magnitude of working power so that the electric power will be effectively used within the range defined by the set demand value. The demand control apparatus of the Japanese Patent Laid-Open No. Sho 57-101526 also cannot change the sequence of preference for loads and select the type of instruments to be controlled. Thus, the demand control apparatus cannot be used in houses, factories and others, depending on various situations. Finally, the control system of Japanese Patent Laid-Open No. Sho 55-103043 can only generate a failure signal without carrying out any actual procedure.
The conventional demand control systems raises a further problem when any one of the loads or instruments is shut off. For example, when a plurality of instruments such as a rice cooker, a water heater, an air conditioner and so on are used in a typical house in the morning, if any one instrument is shut off, it will be very inconvenient.
Energy produced in the power plant of an electric power company is mainly distributed to houses, factories and others. In recent years, the power consumption has greatly changed throughout the year. In general, the power consumption is on peak in the summer daytime while it is off peak in the winter nighttime. The power installation is constructed to cope with the on-peak power consumption.
As the power demand in typical houses increases with the spread of air conditioners, the difference between on-peak and off-peak energy consumption increases. As a result, the annually averaged load or annual load factor for the service capability gradually decreases. The production cost is also increasing. Therefore, the leveling of loads is urgently required.
In order to accomplish the leveling, there has been proposed a system wherein the power supply to loads such as air conditioners is forcedly shut off depending on the need of the energy supplier, irrespective of the customers' needs. Instead, incentive payments are paid back to the customers. For example, in U.S.A., the electric power company computes a tariff from an expected power consumption based on a predicted energy factor for a customer before one day. The computed tariff is one-sidedly reported from the electric power company to the customer. Such a system is called "spot tariff system".
Literature "Actual Proof and Test for concentrically Controlling Loads (Control of Air Conditioners)" in JEC, Convention of Electric Power and Energy Department, 1991 proposed a method for intermittently stopping the power supply to the air conditioners. Although such a method is effective to reduce the on-peak energy consumption, circumstances on the side of houses, factories and others will be completely ignored. Furthermore, the spot tariff system cannot provide a remarkably improved advantage since the predicted demand will not accurately reflect variations in demand due to variable weather. When the air conditioners are intermittently shut off, the leveling of all the loads cannot be effectively accomplished since the instruments to be controlled are limited to the air conditioners.
It is therefore an object of the present invention to provide a demand control apparatus which can properly set the total quantity of working energy for a group of loads below a given level depending on circumstances of houses, factories and so on and to provide a power distribution system which can properly distribute the electric energy and level the loads depending on variations of demand through time and circumstances of houses, factories and other customers.